Planetary gear train of automatic transmission for vehicle

ABSTRACT

A planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting changed torque of the engine, a first planetary gear set, a second planetary gear set, a third planetary gear set, a fourth planetary gear set, a first rotation shaft selectively connected to a transmission housing, a second rotation shaft, a third rotation shaft selectively connected to the transmission housing, a fourth rotation shaft directly connected to the input shaft, a fifth rotation shaft, a sixth rotation shaft selectively connected to the second and fourth rotation shafts, a seventh rotation shaft selectively connected the second rotation shaft, an eighth rotation shaft selectively connected to the seventh rotation shaft, and directly connected to the output shaft, and six friction elements disposed to selectively connect the rotation shafts and selectively connect the rotation shafts with the transmission housing.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2015-0066910 filed May 13, 2015, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an automatic transmission for avehicle. More particularly, the present invention relates to a planetarygear train for an automatic transmission of a vehicle that improvespower delivery performance and reduces fuel consumption by achieving tenforward speed stages or twelve forward speed stages using a minimumnumber of constituent elements.

Description of Related Art

Recently, increasing oil prices have caused vehicle manufacturers allover the world to rush into infinite competition. Particularly in thecase of engines, manufacturers have been pursuing efforts to reduce theweight and improve fuel efficiency of vehicles by reducing engine size,etc.

As a result, research into reduction of weight and enhancement of fuelefficiency through downsizing has been conducted in the case of anengine and research for simultaneously securing operability and fuelefficiency competitiveness through multiple speed stages has beenconducted in the case of an automatic transmission.

However, in the automatic transmission, as the number of transmissionspeed stages increases, the number of internal components alsoincreases, and as a result, the automatic transmission may be difficultto mount, the manufacturing cost and weight may be increased, and powertransmission efficiency may be deteriorated.

Accordingly, development of a planetary gear train which may bring aboutmaximum efficiency with a small number of components may be important inorder to increase a fuel efficiency enhancement effect through themultiple speed stages.

In this aspect, in recent years, 8- and 9-speed automated transmissionshave tended to be achieved, and the research and development of aplanetary gear train capable of implementing more transmission steps hasalso been actively conducted.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing aplanetary gear train of an automatic transmission of a vehicle havingadvantages of improving power delivery performance and fuel economy byachieving ten forward speed stages and one reverse speed stage or twelveforward speed stages and one reverse speed stage using a minimum numberof constituent elements and of improving silent driving using a drivingpoint positioned at a low engine speed.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque of the engine, a first planetary gear set including a first sungear, a first planet carrier, and a first ring gear, a second planetarygear set including a second sun gear, a second planet carrier, and asecond ring gear, a third planetary gear set including a third sun gear,a third planet carrier, and a third ring gear, a fourth planetary gearset including a fourth sun gear, a fourth planet carrier, and a fourthring gear, a first rotation shaft including the first and second sungears and selectively connected to a transmission housing, a secondrotation shaft including the first planet carrier, a third rotationshaft including the first and fourth ring gears and selectivelyconnected to the transmission housing, a fourth rotation shaft includingthe second planet carrier and directly connected to the input shaft, afifth rotation shaft including the second ring gear and the third andfourth sun gears, a sixth rotation shaft including the third planetcarrier and selectively connected to the second and fourth rotationshafts, a seventh rotation shaft including the third ring gear andselectively connected the second rotation shaft, an eighth rotationshaft including the fourth planet carrier and selectively connected tothe seventh rotation shaft, and directly connected to the output shaft,and six friction elements disposed to selectively connect the rotationshafts and selectively connect the rotation shafts with the transmissionhousing.

The first, second, third, and fourth planetary gear sets may be singlepinion planetary gear sets.

The first, second, third, and fourth planetary gear sets may be disposedsequentially from an engine side.

The six friction elements may include a first clutch interposed betweenthe fourth rotation shaft and the sixth rotation shaft, a second clutchinterposed between the seventh rotation shaft and the eighth rotationshaft, a third clutch interposed between the second rotation shaft andthe sixth rotation shaft, a fourth clutch interposed between the secondrotation shaft and the seventh rotation shaft, a first brake interposedbetween the first rotation shaft and the transmission housing, and asecond brake interposed between the third rotation shaft and thetransmission housing.

Shift speed stages achieved by selectively operating the six frictionelements may include a first forward speed stage achieved bysimultaneous operation of the third and fourth clutches and the secondbrake, a second forward speed stage achieved by simultaneous operationof the second and fourth clutches and the second brake, a third forwardspeed stage achieved by simultaneous operation of the second clutch andthe first and second brakes, a fourth forward speed stage achieved bysimultaneous operation of the first and second clutches and the secondbrake, a fifth forward speed stage achieved by simultaneous operation ofthe first and second clutches and the first brake, a sixth forward speedstage achieved by simultaneous operation of the first, second, andfourth clutches, a seventh forward speed stage achieved by simultaneousoperation of the first and fourth clutches and the first brake, aneighth forward speed stage achieved by simultaneous operation of thefirst and third clutches and the first brake, a ninth forward speedstage achieved by simultaneous operation of the third and fourthclutches and the first brake, a tenth forward speed stage achieved bysimultaneous operation of the second and third clutches and the firstbrake, and a reverse speed stage achieved by simultaneous operation ofthe first and third clutches and the second brake.

Shift speed stages achieved by selectively operating the six frictionelements may include a first forward speed stage achieved bysimultaneous operation of the first and third clutches and the secondbrake, a second forward speed stage achieved by simultaneous operationof the third and fourth clutches and the second brake, a third forwardspeed stage achieved by simultaneous operation of the second and thirdclutches and the second brake, a fourth forward speed stage achieved bysimultaneous operation of the second and fourth clutches and the secondbrake, a fifth forward speed stage achieved by simultaneous operation ofthe second clutch and the first and second brakes, a sixth forward speedstage achieved by simultaneous operation of the first and secondclutches and the second brake, a seventh forward speed stage achieved bysimultaneous operation of the first and second clutches and the firstbrake, an eighth forward speed stage achieved by simultaneous operationof the first, second, and fourth clutches, a ninth forward speed stageachieved by simultaneous operation of the first and fourth clutches andthe first brake, a tenth forward speed stage achieved by simultaneousoperation of the first and third clutches and the first brake, aneleventh forward speed stage achieved by simultaneous operation of thethird and fourth clutches and the first brake, a twelfth forward speedstage achieved by simultaneous operation of the second and thirdclutches and the first brake, and a reverse speed stage achieved bysimultaneous operation of the first and fourth clutches and the secondbrake.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque of the engine, a first planetary gear set including a first sungear, a first planet carrier, and a first ring gear, a second planetarygear set including a second sun gear, a second planet carrier, and asecond ring gear, a third planetary gear set including a third sun gear,a third planet carrier, and a third ring gear, a fourth planetary gearset including a fourth sun gear, a fourth planet carrier, and a fourthring gear, a first clutch selectively connecting the second planetcarrier and the third planet carrier, a second clutch selectivelyconnecting the third ring gear and the fourth planet carrier, a thirdclutch selectively connecting the first planet carrier and the thirdplanet carrier, a fourth clutch selectively connecting the first planetcarrier and the third ring gear, a first brake selectively connectingthe first and second sun gears and the transmission housing, and asecond brake selectively connecting the first ring gear and thetransmission housing, in which the input shaft may be directly connectedto the second planet carrier, the output shaft may be directly connectedto the fourth planet carrier, the first sun gear may be directlyconnected to the second sun gear, the first ring gear may be directlyconnected to the fourth ring gear, and the second ring gear and thethird sun gear may be directly connected to the fourth sun gear.

Various embodiments of the present invention may achieve ten forwardspeed stages or twelve forward speed stages by combining four planetarygear sets which are formed of simple planetary gear sets with sixfriction elements. Therefore, power delivery performance and fueleconomy may be improved.

Also, silent drivability of vehicle may be improved greatly through themultiple speed stages of the automatic transmission appropriate to theengine rotation speed.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g., fuel derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example, bothgasoline-powered and electric-powered vehicles.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an exemplary planetary gear trainaccording to the present invention.

FIG. 2 is an operation chart of friction elements at each speed stage inthe exemplary planetary gear train according to the present inventionfor achieving ten forward speed stages and one reverse speed stage.

FIG. 3 is an operation chart of friction elements at each speed stage inthe exemplary planetary gear train according to the present inventionfor achieving twelve forward speed stages and one reverse speed stage.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

FIG. 1 is a configuration diagram of a planetary gear train according tovarious embodiments of the present invention.

Referring to FIG. 1, the planetary gear train according to variousembodiments of the present invention includes first, second, third, andfourth planetary gear sets PG1, PG2, PG3, and PG4 disposed on the sameaxis, and an input shaft IS, an output shaft OS, eight rotation shaftsTM1 to TM8 directly connecting to each other and respective rotationelements of the first, second, third, and fourth planetary gear setsPG1, PG2, PG3, and PG4, six friction elements C1 to C4 and B1 to B2, anda transmission housing H.

As a result, torque input from the input shaft IS is transmitted by aninter-complementation operation of the first, second, third, and fourthplanetary gear sets PG1, PG2, PG3, and PG4 to be output through theoutput shaft OS.

The respective simple planetary gear sets are disposed in a sequence ofthe first, second, third, and fourth planetary gear sets PG1, PG2, PG3,and PG4 from an engine side.

The input shaft IS is an input member, and rotational power from acrankshaft of an engine is torque-converted through a torque converterto be input into the input shaft IS.

The output shaft OS is an output member, is disposed on the same axis asthe input shaft IS, and transfers transmitted driving torque to adriving shaft through a differential apparatus.

The first planetary gear set PG1 as a single-pinion planetary gear setincludes a first sun gear S1, a first planetary carrier PC 1 thatsupports a first pinion P1 which outer-engages with the first sun gearS1, and a first ring gear R1 which inner-engages with the first pinionP1 as rotation elements.

The second planetary gear set PG2 as a single-pinion planetary gear setincludes a second sun gear S2, a second planetary carrier PC2 thatsupports a second pinion P2 which outer-engages with the second sun gearS2, and a second ring gear R2 which inner-engages with the second pinionP2.

The third planetary gear set PG3 as a single-pinion planetary gear setincludes a third sun gear S3, a third planetary carrier PC3 thatsupports a third pinion P3 which outer-engages with the third sun gearS3, and a third ring gear R3 which inner-engages with the third pinionP3.

The fourth planetary gear set PG4 as a single-pinion planetary gear setincludes a fourth sun gear S4, a fourth planetary carrier PC4 thatsupports a fourth pinion P4 which outer-engages with the fourth sun gearS4, and a fourth ring gear R4 which inner-engages with the fourth pinionP4.

In the first, second, third, and fourth planetary gear sets PG1, PG2,PG3, and PG4, one or more rotation elements are directly connected toeach other to operate with a total of eight rotational shafts TM1 toTM8.

Configurations of the eight rotational shafts TM1 to TM8 will bedescribed below.

The first rotation shaft TM1 includes the first and second sun gears S1and S2, and is selectively connected to the transmission housing H.

The second rotation shaft TM2 includes the first planet carrier PC1.

The third rotation shaft TM3 includes the first and fourth ring gears R1and R4, and is selectively connected to the transmission housing H.

The fourth rotation shaft TM4 includes the second planet carrier PC1,and is directly connected to the input shaft IS so as to always beoperated as an input element.

The fifth rotation shaft TM5 includes the second ring gear R2 and thethird and fourth sun gears S3 and S4.

The sixth rotation shaft TM6 includes the third planet carrier PC3, andis selectively connected to the second rotation shaft TM2 and the fourthrotation shaft TM4.

The seventh rotation shaft TM7 includes the third ring gear R3, and isselectively connected to the second rotation shaft TM2.

The eighth rotation shaft TM8 includes the fourth planet carrier PC4, isselectively connected to the seventh rotation shaft TM7, and is directlyconnected to the output shaft OS so as to always be operated as anoutput element.

In addition, among the rotation shafts TM1-TM8, four clutches C1, C2,C3, and C4 which are friction elements are disposed at connectionportions where the rotation shafts are connected to each other.

In addition, among the rotational shafts TM1 to TM8, two brakes B1 andB2 which are friction elements are disposed at connection portionsbetween any one rotation shaft and the transmission housing H.

The six frictional elements C1 to C4 and B1 and B2 will be described infurther detail.

The first clutch C1 is interposed between the fourth rotation shaft TM4and the sixth rotation shaft TM6, and selectively connects the fourthrotation shaft TM4 and the sixth rotation shaft TM6.

The second clutch C2 is interposed between the seventh rotation shaftTM7 and the eighth rotation shaft TM8, and selectively connects theseventh rotation shaft TM7 and the eighth rotation shaft TM8.

The third clutch C3 is interposed between the second rotation shaft TM2and the sixth rotation shaft TM6, and selectively connects the secondrotation shaft TM2 and the sixth rotation shaft TM6.

The fourth clutch C4 is interposed between the second rotation shaft TM2and the seventh rotation shaft TM7, and selectively connects the secondrotation shaft TM2 and the seventh rotation shaft TM7.

The first brake B1 is interposed between the first rotation shaft TM1and the transmission housing H, and selective causes the first rotationshaft TM1 to be operated as a fixed element.

The second brake B2 is interposed between the third rotation shaft TM3and the transmission housing H, and selective causes the third rotationshaft TM3 to be operated as a fixed element.

The friction elements including the first, second, third, and fourthclutches C1, C2, C3, and C4 and the first and second brakes B1 and B2may be multi-plate friction elements of a wet type that are operated byhydraulic pressure.

FIG. 2 is an operation chart of friction elements at each speed stage inthe planetary gear train according to various embodiments of the presentinvention for achieving ten forward speed stages and one reverse speedstage.

As shown in FIG. 2, three friction elements are operated at each speedstage in the planetary gear train according to various embodiments ofthe present invention.

A first forward speed stage 1ST is achieved by simultaneous operation ofthe third and fourth clutches C3 and C4 and the second brake B2.

A second forward speed stage 2ND is achieved by simultaneous operationof the second and fourth clutches C2 and C4 and the second brake B2.

A third forward speed stage 2ND is achieved by simultaneous operation ofthe second clutch C2 and the first and second brakes B1 and B2.

A fourth forward speed stage 4TH is achieved by simultaneous operationof the first and second clutches C1 and C2 and the second brake B2.

A fifth forward speed stage 5TH is achieved by simultaneous operation ofthe first and second clutches C1 and C2 and the first brake B1.

A sixth forward speed stage 6TH is achieved by simultaneous operation ofthe first, second, and fourth clutches C1, C2, and C4.

A seventh forward speed stage 7TH is achieved by simultaneous operationof the first and fourth clutches C1 and C4 and the first brake B1.

An eighth forward speed stage 8TH is achieved by simultaneous operationof the first and third clutches C1 and C3 and the first brake B1.

A ninth forward speed stage 9TH is achieved by simultaneous operation ofthe third and fourth clutches C3 and C4 and the first brake B1.

A tenth forward speed stage 10TH is achieved by simultaneous operationof the second and third clutches C2 and C3 and the first brake B1.

A reverse speed stage REV is achieved by simultaneous operation of thefirst and third clutches C1 and C3 and the second brake B2.

The shifting processes will be described in further detail.

The third and fourth clutches C3 and C4 and the second brake B2 aresimultaneously operated at the first forward speed stage 1ST. In a statein which the second rotation shaft TM2 is connected to the sixth andseventh rotation shafts TM6 and TM7, the input is made into the fourthrotation shaft TM4, and the third rotation shaft TM3 is operated as thefixed elements, the first forward speed stage 1ST is achieved.

The second and fourth clutches C2 and C4 and the second brake B2 aresimultaneously operated at the second forward speed stage 2ND. In astate in which the second rotation shaft TM2 is connected to the seventhrotation shaft TM7, the seventh rotation shaft TM7 is connected to theeighth rotation shaft TM8, the input is made into the fourth rotationshaft TM4, and the third rotation shaft TM3 is operated as the fixedelement, the second forward speed stage 2ND is achieved.

The second clutch C2 and the first and second brakes B1 and B2 aresimultaneously operated at the third forward speed stage 3RD. In a statein which the seventh rotation shaft TM7 is connected to the eighthrotation shaft TM8, the input is made into the fourth rotation shaftTM4, and the first and third rotation shafts TM1 and TM3 are operated asthe fixed element, the third forward speed stage 3RD is achieved.

The first and second clutches C1 and C2 and the second brake B2 aresimultaneously operated at the fourth forward speed stage 4TH. In astate in which the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6, the seventh rotation shaft TM7 is connected to theeighth rotation shaft TM8, the input is made into the fourth rotationshaft TM4, and the third rotation shaft TM3 is operated as the fixedelement, the fourth forward speed stage 4TH is achieved.

The first and second clutches C1 and C2 and the first brake B1 aresimultaneously operated at the fifth forward speed stage 5TH. In a statein which the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6, the seventh rotation shaft TM7 is connected theeighth rotation shaft TM8, the input is made into the fourth rotationshaft TM4, and the first rotation shaft TM1 is operated as the fixedelement, the fifth forward speed stage 5TH is achieved.

The first, second, fourth clutches C1, C2, and C4 are simultaneouslyoperated at the sixth forward speed stage 6TH. In a state in which thefourth rotation shaft TM4 is connected to the sixth rotation shaft TM6,the second rotation shaft TM2 is connected to the seventh rotation shaftTM7, the seventh rotation shaft TM7 is connected to the eighth rotationshaft TM8, and the input is made into the fourth rotation shaft TM4, thesixth forward speed stage 6TH for just outputting the input is achievedas all of the first, second, third, and fourth planetary gear sets PG1,PG2, PG3, and PG4 integrally rotate at the same speed.

The first and fourth clutches C1 and C4 and the first brake B1 aresimultaneously operated at the seventh forward speed stage 7TH. In astate in which the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6, the second rotation shaft TM2 is connected to theseventh rotation shaft TM7, the input is made into the fourth rotationshaft TM4, and the first rotation shaft TM1 is operated as the fixedelement, the seventh forward speed stage 7TH is achieved.

The first and third clutches C1 and C3 and the first brake B1 aresimultaneously operated at the eighth forward speed stage 8TH. In astate in which the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6, the second rotation shaft TM2 is connected to thesixth rotation shaft TM6, the input is made into the fourth rotationshaft TM4, and the first rotation shaft TM1 is operated as the fixedelement, the eighth forward speed stage 8TH is achieved.

The third and fourth clutches C3 and C4 and the first brake B1 aresimultaneously operated at the ninth forward speed stage 9TH. In a statein which the second rotation shaft TM2 is connected to the sixth andseventh rotation shafts TM6 and TM7, the input is made into the fourthrotation shaft TM4, and the first rotation shaft TM1 is operated as thefixed element, the ninth forward speed stage 9TH is achieved.

The second and third clutches C2 and C3 and the first brake B1 aresimultaneously operated at the tenth forward speed stage 10TH. In astate in which the second rotation shaft TM2 is connected the sixthrotation shaft TM6, and seventh rotation shaft TM7 is connected to theeighth rotation shaft TM8, the input is made into the fourth rotationshaft TM4, and the first rotation shaft TM1 is operated as the fixedelement, the tenth forward speed stage 10TH is achieved.

The first and third clutches C1 and C3 and the second brake B2 aresimultaneously operated at the reverse speed stage REV. In a state inwhich the sixth rotation shaft TM6 is connected to the second and fourthrotation shafts TM2 and TM4, the input is made into the fourth rotationshaft TM4, and the third rotation shaft TM3 is operated as the fixedelement, the reverse speed stage REV is achieved.

The planetary gear train according to various embodiments of the presentinvention may achieve ten forward speed stages and one reverse speedstage by control of four planetary gear sets PG1, PG2, PG3, and PG4,four clutches C1, C2, C3, and C4, and two brakes B1 and B2.

FIG. 3 is an operation chart of friction elements at each speed stage inthe planetary gear train according to various embodiments of the presentinvention for achieving twelve forward speed stages and one reversespeed stage.

As shown in FIG. 3, three friction elements are operated at each speedstage even while shifting twelve forward speed stages and one reversespeed stage.

A first forward speed stage 1ST is achieved by simultaneous operation ofthe first and third clutches C1 and C3 and the second brake B1.

The second forward speed stage 2ND is achieved by simultaneous operationof the third and fourth clutches C3 and C4 and the second brake B2.

The third forward speed stage 3RD is achieved by simultaneous operationof the second and third clutches C2 and C3 and the second brake B2.

The fourth forward speed stage 4TH is achieved by simultaneous operationof the second and fourth clutches C2 and C4 and the second brake B2.

The fifth forward speed stage 5TH is achieved by simultaneous operationof the second clutch C2 and the first and second brakes B1 and B2.

The sixth forward speed stage 6TH is achieved by simultaneous operationof the first and second clutches C1 and C2 and the second brake B2.

The seventh forward speed stage 7TH is achieved by simultaneousoperation of the first and second clutches C1 and C2 and the first brakeB1.

The eighth forward speed stage 8TH is achieved by simultaneous operationof the first, second, and fourth clutches C1, C2, and C4.

The ninth forward speed stage 9TH is achieved by simultaneous operationof the first and fourth clutches C1 and C4 and the first brake B1.

The tenth forward speed stage 10TH is achieved by simultaneous operationof the first and third clutches C1 and C3 and the first brake B1.

The eleventh forward speed stage 11TH is achieved by simultaneousoperation of the third and fourth clutches C3 and C4 and the first brakeB1.

The twelfth forward speed stage 12TH is achieved by simultaneousoperation of the second and third clutches C2 and C3 and the first brakeB1.

The reverse speed stage REV is achieved by simultaneous operation of thefirst and fourth clutches C1 and C4 and the second brake B2.

The shifting processes will be described in further detail.

The first and third clutches C1 and C3 and the second brake B2 aresimultaneously operated at the first forward speed stage 1ST. In a statein which the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6, the second rotation shaft TM2 is connected to theseventh rotation shaft TM7, the input is made into the fourth rotationshaft TM4, and the third rotation shaft TM3 is operated as the fixedelement, the first forward speed stage 1ST is achieved.

The third and fourth clutches C3 and C4 and the second brake B2 aresimultaneously operated at the second forward speed stage 2ND. In astate in which the second rotation shaft TM2 is connected to the sixthand seventh rotation shafts TM6 and TM7, the input is made into thefourth rotation shaft TM4, and the third rotation shaft TM3 is operatedas the fixed element, the second forward speed stage 2ND is achieved.

The second and third clutches C2 and C3 and the second brake B2 aresimultaneously operated at the third forward speed stage 3RD. In a statein which the second rotation shaft TM2 is connected to the sixthrotation shaft TM6, the seventh rotation shaft TM7 is connected to theeighth rotation shaft TM8, the input is made into the fourth rotationshaft TM4, and the third rotation shaft TM3 is operated as the fixedelement, the third forward speed stage 3RD is achieved.

The second and fourth clutches C2 and C4 and the second brake B2 aresimultaneously operated at the fourth forward speed stage 4TH. In astate in which the second rotation shaft TM2 is connected to the seventhrotation shaft TM7, the seventh rotation shaft TM7 is connected to theeighth rotation shaft TM8, the input is made into the fourth rotationshaft TM4, and the third rotation shaft TM3 is operated as the fixedelement, the fourth forward speed stage 4TH is achieved.

The second clutch C2 and the first and second brakes B1 and B2 aresimultaneously operated at the fifth forward speed stage 5TH. In a statein which the seventh rotation shaft TM7 is connected to the eighthrotation shaft TM8, the input is made into the fourth rotation shaftTM4, and the first and second rotation shafts TM1 and TM2 are operatedas the fixed element, the fifth forward speed stage 5TH is achieved.

The first and second clutches C1 and C2 and the second brake B2 aresimultaneously operated at the sixth forward speed stage 6TH. In a statein which the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6, the seventh rotation shaft TM7 is connected to theeighth rotation shaft TM8, the input is made into the fourth rotationshaft TM4, and the third rotation shaft TM3 is operated as the fixedelement, the sixth forward speed stage 6TH is achieved.

The first and second clutches C1 and C2 and the first brake B1 aresimultaneously operated at the seventh forward speed stage 7TH. In astate in which the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6, the seventh rotation shaft TM7 is connected to theeighth rotation shaft TM8, input is made into the fourth rotation shaftTM4, and the first rotation shaft TM1 is operated as the fixed element,the seventh forward speed stage 7TH is achieved.

The first, second, and fourth clutches C1, C2, and C4 are simultaneouslyoperated at the eighth forward speed stage 8TH. In a state in which thefourth rotation shaft TM4 is connected to the sixth rotation shaft TM6,the second rotation shaft TM2 is connected to the seventh rotation shaftTM7, the seventh rotation shaft TM7 is connected to the eighth rotationshaft TM8, and the input is made into the fourth rotation shaft TM4, theeighth forward speed stage 8TH for just outputting the input is achievedas all of the first, second, third, and fourth planetary gear sets PG1,PG2, PG3, and PG4 integrally rotate at the same speed.

The first and fourth clutches C1 and C4 and the first brake B1 aresimultaneously operated at the ninth forward speed stage 9TH. In a statein which the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6, the second rotation shaft TM2 is connected to theseventh rotation shaft TM7, the input is made into the fourth rotationshaft TM4, and the first rotation shaft TM1 is operated as the fixedelement, the ninth forward speed stage 9TH is achieved.

The first and third clutches C1 and C3 and the first brake B1 aresimultaneously operated at the tenth forward speed stage 10TH. In astate in which the fourth rotation shaft TM4 is connected to the sixthrotation shaft TM6, the second rotation shaft TM2 is connected to thesixth rotation shaft TM6, the input is made into the fourth rotationshaft TM4, and the first rotation shaft TM1 is operated as the fixedelement, the tenth forward speed stage 10TH is achieved.

The third and fourth clutches C3 and C4 and the first brake B1 aresimultaneously operated at the eleventh forward speed stage 11TH. In astate in which the second rotation shaft TM2 is connected to the sixthand seventh rotation shafts TM6 and TM7, the input is made into thefourth rotation shaft TM4, and the first rotation shaft TM1 is operatedas the fixed element, the eleventh forward speed stage 11TH is achieved.

The second and third clutches C2 and C3 and the first brake B1 aresimultaneously operated at the twelfth forward speed stage 12TH. In astate in which the second rotation shaft TM2 is connected to the sixthrotation shaft TM6, the seventh rotation shaft TM7 is connected to theeighth rotation shaft TM8, the input is made into the fourth rotationshaft TM4, and the first rotation shaft TM1 is operated as the fixedelement, the twelfth forward speed stage 12TH is achieved.

The first and fourth clutches C1 and C4 and the second brake B2 aresimultaneously operated at the reverse speed stage REV. In a state inwhich the fourth rotation shaft TM4 is connected to the sixth rotationshaft TM6, the second rotation shaft TM2 is connected to the seventhrotation shaft TM7, the input is made into the fourth rotation shaftTM4, and the third rotation shaft TM3 is operated as the fixed element,the reverse speed stage REV is achieved.

The planetary gear train according to various embodiments of the presentinvention may achieve twelve forward speed stages and one reverse speedstage by control of four planetary gear sets PG1, PG2, PG3, and PG4,four clutches C1, C2, C3, and C4, and two brakes B1 and B2.

The planetary gear train according to various embodiments of the presentinvention may improve the power transmission efficiency and the fuelefficiency through the multiple speed stages of the automatictransmission.

Since a speed stage suitable to engine speed can be achieved due tomultiple speed stages, silent driving may be improved.

In addition, since three friction elements operate at each speed and thenumber of non-operating friction elements is minimized, a friction dragloss is decreased. Therefore, drag torque and power loss may be reduced.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A planetary gear train of an automatic transmission for a vehicle, comprising: an input shaft receiving torque of an engine; an output shaft outputting changed torque of the engine; a first planetary gear set including a first sun gear, a first planet carrier, and a first ring gear; a second planetary gear set including a second sun gear, a second planet carrier, and a second ring gear; a third planetary gear set including a third sun gear, a third planet carrier, and a third ring gear; a fourth planetary gear set including a fourth sun gear, a fourth planet carrier, and a fourth ring gear; a first rotation shaft including the first and second sun gears and selectively connected to a transmission housing; a second rotation shaft including the first planet carrier; a third rotation shaft including the first and fourth ring gears and selectively connected to the transmission housing; a fourth rotation shaft including the second planet carrier and directly connected to the input shaft; a fifth rotation shaft including the second ring gear and the third and fourth sun gears; a sixth rotation shaft including the third planet carrier and selectively connected to the second and fourth rotation shafts; a seventh rotation shaft including the third ring gear and selectively connected the second rotation shaft; an eighth rotation shaft including the fourth planet carrier and selectively connected to the seventh rotation shaft, and directly connected to the output shaft; and six friction elements, wherein each of the six friction elements are disposed to selectively connect at least one of the first to eighth rotation shafts with another rotation shaft of the first to eighth rotation shafts or the transmission housing, wherein the six friction elements comprise: a first clutch interposed between the fourth rotation shaft and the sixth rotation shaft; a second clutch interposed between the seventh rotation shaft and the eighth rotation shaft; a third clutch interposed between the second rotation shaft and the sixth rotation shaft; a fourth clutch interposed between the second rotation shaft and the seventh rotation shaft; a first brake interposed between the first rotation shaft and the transmission housing; and a second brake interposed between the third rotation shaft and the transmission housing.
 2. The planetary gear train of claim 1, wherein the first, second, third, and fourth planetary gear sets comprise single pinion planetary gear sets.
 3. The planetary gear train of claim 1, wherein the first, second, third, and fourth planetary gear sets are disposed sequentially from an engine side.
 4. The planetary gear train of claim 1, wherein shift speed stages are achieved by selectively operating the six friction elements and comprise: a first forward speed stage achieved by simultaneous operation of the third and fourth clutches and the second brake; a second forward speed stage achieved by simultaneous operation of the second and fourth clutches and the second brake; a third forward speed stage achieved by simultaneous operation of the second clutch and the first and second brakes; a fourth forward speed stage achieved by simultaneous operation of the first and second clutches and the second brake; a fifth forward speed stage achieved by simultaneous operation of the first and second clutches and the first brake; a sixth forward speed stage achieved by simultaneous operation of the first, second, and fourth clutches; a seventh forward speed stage achieved by simultaneous operation of the first and fourth clutches and the first brake; an eighth forward speed stage achieved by simultaneous operation of the first and third clutches and the first brake; a ninth forward speed stage achieved by simultaneous operation of the third and fourth clutches and the first brake; a tenth forward speed stage achieved by simultaneous operation of the second and third clutches and the first brake; and a reverse speed stage achieved by simultaneous operation of the first and third clutches and the second brake.
 5. The planetary gear train of claim 1, wherein shift speed stages achieved by selectively operating the six friction elements comprise: a first forward speed stage achieved by simultaneous operation of the first and third clutches and the second brake; a second forward speed stage achieved by simultaneous operation of the third and fourth clutches and the second brake; a third forward speed stage achieved by simultaneous operation of the second and third clutches and the second brake; a fourth forward speed stage achieved by simultaneous operation of the second and fourth clutches and the second brake; a fifth forward speed stage achieved by simultaneous operation of the second clutch and the first and second brakes; a sixth forward speed stage achieved by simultaneous operation of the first and second clutches and the second brake; a seventh forward speed stage achieved by simultaneous operation of the first and second clutches and the first brake; an eighth forward speed stage achieved by simultaneous operation of the first, second, and fourth clutches; a ninth forward speed stage achieved by simultaneous operation of the first and fourth clutches and the first brake; a tenth forward speed stage achieved by simultaneous operation of the first and third clutches and the first brake; an eleventh forward speed stage achieved by simultaneous operation of the third and fourth clutches and the first brake; a twelfth forward speed stage achieved by simultaneous operation of the second and third clutches and the first brake; and a reverse speed stage achieved by simultaneous operation of the first and fourth clutches and the second brake.
 6. A planetary gear train of an automatic transmission for a vehicle, comprising: an input shaft receiving torque of an engine; an output shaft outputting changed torque of the engine; a first planetary gear set including a first sun gear, a first planet carrier, and a first ring gear; a second planetary gear set including a second sun gear, a second planet carrier, and a second ring gear; a third planetary gear set including a third sun gear, a third planet carrier, and a third ring gear; a fourth planetary gear set including a fourth sun gear, a fourth planet carrier, and a fourth ring gear; a first clutch selectively connecting the second planet carrier and the third planet carrier; a second clutch selectively connecting the third ring gear and the fourth planet carrier; a third clutch selectively connecting the first planet carrier and the third planet carrier; a fourth clutch selectively connecting the first planet carrier and the third ring gear; a first brake selectively connecting the first and second sun gears and the transmission housing; and a second brake selectively connecting the first ring gear and the transmission housing, wherein the input shaft is directly connected to the second planet carrier, the output shaft is directly connected to the fourth planet carrier, the first sun gear is directly connected to the second sun gear, the first ring gear is directly connected to the fourth ring gear, and the second ring gear and the third sun gear are directly connected to the fourth sun gear.
 7. The planetary gear train of claim 6, wherein the first, second, third, and fourth planetary gear sets comprise single pinion planetary gear sets.
 8. The planetary gear train of claim 6, wherein the first, second, third, and fourth planetary gear sets are disposed sequentially from an engine side.
 9. The planetary gear train of claim 6, wherein shift speed stages that are achieved by selectively operating the first, second, third, and fourth clutches and the first and second brakes comprise: a first forward speed stage achieved by simultaneous operation of the third and fourth clutches and the second brake; a second forward speed stage achieved by simultaneous operation of the second and fourth clutches and the second brake; a third forward speed stage achieved by simultaneous operation of the second clutch and the first and second brakes; a fourth forward speed stage achieved by simultaneous operation of the first and second clutches and the second brake; a fifth forward speed stage achieved by simultaneous operation of the first and second clutches and the first brake; a sixth forward speed stage achieved by simultaneous operation of the first, second, and fourth clutches; a seventh forward speed stage achieved by simultaneous operation of the first and fourth clutches and the first brake; an eighth forward speed stage achieved by simultaneous operation of the first and third clutches and the first brake; a ninth forward speed stage achieved by simultaneous operation of the third and fourth clutches and the first brake; a tenth forward speed stage achieved by simultaneous operation of the second and third clutches and the first brake; and a reverse speed stage achieved by simultaneous operation of the first and third clutches and the second brake.
 10. The planetary gear train of claim 6, wherein shift speed stages that are achieved by selectively operating the first, second, third, and fourth clutches and the first and second brakes comprise: a first forward speed stage achieved by simultaneous operation of the first and third clutches and the second brake; a second forward speed stage achieved by simultaneous operation of the third and fourth clutches and the second brake; a third forward speed stage achieved by simultaneous operation of the second and third clutches and the second brake; a fourth forward speed stage achieved by simultaneous operation of the second and fourth clutches and the second brake; a fifth forward speed stage achieved by simultaneous operation of the second clutch and the first and second brakes; a sixth forward speed stage achieved by simultaneous operation of the first and second clutches and the second brake; a seventh forward speed stage achieved by simultaneous operation of the first and second clutches and the first brake; an eighth forward speed stage achieved by simultaneous operation of the first, second, and fourth clutches; a ninth forward speed stage achieved by simultaneous operation of the first and fourth clutches and the first brake; a tenth forward speed stage achieved by simultaneous operation of the first and third clutches and the first brake; an eleventh forward speed stage achieved by simultaneous operation of the third and fourth clutches and the first brake; a twelfth forward speed stage achieved by simultaneous operation of the second and third clutches and the first brake; and a reverse speed stage achieved by simultaneous operation of the first and fourth clutches and the second brake. 